Previously established human lung carcinoma Lx-1 has been investigated. The existence of tumor cell heterogeneity in human lung carcinoma Lx-1 has been demonstrated by morphology and by differential drug sensitivity of its four subclones isolated in culture. In collaboration with Dr. R. E. Parks, Jr., an effective combination chemotherapy has been established based on the finding that formation of biologically nucleotides of the adenosine analogs is greatly increased by pretreatment of cells with 2'-deoxycoformycin (dCF). In culture, dCF pretreatment for 15 minutes greatly potentiates 8-Azadenosine (8-Aza-Ado) activity against human lung carcinoma Lx-1 and its four subclones with varying degrees of sensitivity. The in vivo studies using ATS-mouse xenografts showed that dCF (0.025 mg/Kg/day x 1) one hour pretreatment, followed by 8-Aza-Ado (40 mg/Kg/dayx1) significantly reduced the tumor weight to 35% of the untreated control while 8-Aza-Ado alone had no effect. This combination given on days one three completely inhibits tumor growth with no sign of toxicity as animals gained weight. The combination of dCF and Ara-A against Lx-1 and its four subclones was carried out in culture and in ATS-mouse xenografts. The in vitro drug sensitivity studies of malignant effusion from a patient with pancreatic tumor showed that after 24 hours of incubation, Adriamycin at 10 to the minus 5th power M caused a 60% decrease in cell number when compared to the untreated control. At an equal molar concentration (10 to the minus 5th power M) 5-FU and BCNU decreased the cell number by only 14 and 21% respectively. The patient achieved a partial response with single agent, Adriamycin.